DESCRIPTION

This module provides easy access to configuration data stored in an XML file. Configuration is retrieved using XPath keys; various methods exist to convert the result to a variety of convenient forms.

If the methods are called as static functions (as opposed to as object methods) then they access data stored in the default configuration file (details given below).

Subconfigurations

By default, the XPath context is at the root node of the XML document. If some other context is required, then a subconfiguration object can be used. This is a child Config::XPath object, built from an XPath query on the parent. Whatever node the query matches becomes the context for the new object. The methods get_sub() and get_sub_list() perform this task; the former returning a single child, and the latter returning a list of all matches.

CONSTRUCTOR

$conf = Config::XPath->new( %args )

This function returns a new instance of a Config::XPath object, containing the configuration in the named XML file. If the given file does not exist, or an error occured while reading it, an exception is thrown.

The %args hash requires one the following keys to provide the XML source:

filename => $file

The filename of the XML file to read

xml => $xml

A string containing XML data

ioref => IO

An IO handle reference

Also may be provided:

parser => $parser

An XML::Parser object

If a parser is not provided, one will be constructed internally.

METHODS

$result = $config->get( $paths, %args )

This method retrieves the result of one of more XPath expressions from the XML file. Each expression should give either a text-valued element with no sub-elements, an attribute, or an XPath function that returns a string, integer or boolean value.

The $paths argument should contain a data tree of ARRAY and HASH references, whose leaves will be the XPath expressions used. The $result will be returned in a similar tree structure, with the leaves containing the value each expression yielded against the XML config. The %args may contain a default key, which should give default values for these results, also in a similar tree structure.

If no suitable node was found matching an XPath expression and no corresponding default value is found, then an exception is thrown. If more than one node is returned, or the returned node is not either a plain-text content containing no child nodes, or an attribute, then an exception is thrown.

A hash that may contain extra options to control the operation. Supports the following keys:

default

Contains a tree in the same structure as the $paths, whose leaf values should be returned instead of the value yielded by the XPath expression, in the case that no nodes match it.

$str = $config->get_string( $path, %args )

This function is a smaller version of the get method, which only works on a single string path.

$path

The XPath to the required configuration node

%args

A hash that may contain extra options to control the operation. Supports the following keys:

default

If no XML node is found matching the path, return this value rather than throwing an exception.

$attrs = $config->get_attrs( $path )

This method retrieves the attributes of a single element in the XML file. The attributes are returned in a hash, along with the name of the element itself, which is returned in a special key named '+'. This name is not valid for an XML attribute, so this key will never clash with an actual value from the XML file.

If no suitable node was found matching the XPath query, then an exception is thrown. If more than one node matched, or the returned node is not an element, then an exception is thrown.

$path

The XPath to the required configuration node

@results = $config->get_list( $listpath; $valuepaths, %args )

This method obtains a list of nodes matching the $listpath expression. For each node in the list, it obtains the result of the $valuepaths with the XPath context at each node, and returns them all in a list. The $valuepaths argument can be a single string expression, or an ARRAY or HASH tree, as for the get() method.

If the $valuepaths argument is not supplied, the type of each node determines the value that will be returned. Element nodes return a hashref, identical to that which get_attrs() returns. Other nodes will return their XPath string value.

$listpath

The XPath expression to generate the list of nodes.

$valuepaths

Optional. If present, the XPath expression or tree of expressions to generate the results.

%args

A hash that may contain extra options to control the operation. Supports the following keys:

default

Contains a tree in the same structure as the $valuepaths, whose leaf values should be returned instead of the value yielded by the XPath expression, in the case that no nodes match it.

$map = $config->get_map( $listpath, $keypath, $valuepaths, %args )

This method obtains a map, returned as a hash, containing one entry for each node returned by the $listpath search, where the key and value are given by the $keypath and $valuepaths within each node. It is not an error for no nodes to match the $listpath.

The result of the $listpath query must be a nodeset. The result of the $keypath is used as the hash key for each node, and must be convertable to a string, by the same rules as the get_string() method. The value for each node in the hash will be obtained using the $valuepaths, which can be a plain string, or an ARRAY or HASH tree, as for the get() method.

The keys obtained by the $keypath should be unique. In the case of duplicates, the last value from the nodeset is used.

$listpath

The XPath to generate the nodeset

$keypath

The XPath within each node to generate the key

$valuepaths

The XPath expression or tree of expressions within each node to generate the value.

%args

A hash that may contain extra options to control the operation. Supports the following keys:

default

Contains a tree in the same structure as the $valuepaths, whose leaf values should be returned instead of the value yielded by the XPath expression, in the case that no nodes match it.

$subconfig = $config->get_sub( $path )

This method constructs a new Config::XPath object whose context is at the single node selected by the XPath query. The newly constructed child object is then returned.

If no suitable node was found matching the XPath query, then an exception of is thrown. If more than one node matched, then an exception is thrown.

$path

The XPath to the required configuration node

@subconfigs = $config->get_sub_list( $path )

This method constructs a list of new Config::XPath objects whose context is at each node selected by the XPath query. The array of newly constructed objects is then returned. Unlike other methods, it is not an error for no nodes to match.

$path

The XPath for the required configuration

DEFAULT CONFIG FILE

In the case of calling as static functions, the default configuration is accessed. When the module is loaded no default configuration exists, but one can be loaded by calling the read_default_config() function. This makes programs simpler to write in cases where only one configuration file is used by the program.

read_default_config( $file )

This function reads the default configuration file, from the location given. If the file is not found, or an error occurs while reading it, then an exception is thrown.

The default configuration is cached, so multiple calls to this function will not result in multiple reads of the file; subsequent requests will be silently ignored, even if a different filename is given.

$file

The filename of the default configuration to load

FUNCTIONS

Each of the following functions is equivalent to a similar method called on the default configuration, as loaded by read_default_config().